Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932531AbXAAXxJ (ORCPT ); Mon, 1 Jan 2007 18:53:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932512AbXAAXxJ (ORCPT ); Mon, 1 Jan 2007 18:53:09 -0500 Received: from rtr.ca ([64.26.128.89]:4278 "EHLO mail.rtr.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932531AbXAAXxI (ORCPT ); Mon, 1 Jan 2007 18:53:08 -0500 X-Greylist: delayed 1461 seconds by postgrey-1.27 at vger.kernel.org; Mon, 01 Jan 2007 18:53:08 EST Message-ID: <4599992D.8000607@rtr.ca> Date: Mon, 01 Jan 2007 18:28:45 -0500 From: Mark Lord User-Agent: Thunderbird 1.5.0.9 (X11/20061206) MIME-Version: 1.0 To: jens.axboe@oracle.com Cc: Rene Herman , Tejun Heo , Alan Cox , linux-kernel@vger.kernel.org, Linus Torvalds Subject: Re: 2.6.20-rc2+: CFQ halving disk throughput. References: <45893CAD.9050909@gmail.com> <45921E73.1080601@gmail.com> <4592B25A.4040906@gmail.com> <45932AF1.9040900@gmail.com> <45998F62.6010904@gmail.com> In-Reply-To: <45998F62.6010904@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1495 Lines: 40 Rene Herman wrote: > Tejun Heo wrote: > >> Everything seems fine in the dmesg. Performance degradation is >> probably some other issue in -rc kernel. I'm suspecting recently >> fixed block layer bug. If it's still the same in the next -rc, >> please report. > > In fact, it's CFQ. The PATA thing was a red herring. 2.6.20-rc2 and 3 > give me ~ 24 MB/s from "hdparm t /dev/hda" while 2.6.20-rc1 and below > give me ~ 50 MB/s. > > Jens: this is due to "[PATCH] cfq-iosched: tighten allow merge > criteria", 719d34027e1a186e46a3952e8a24bf91ecc33837: > > http://www2.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=719d34027e1a186e46a3952e8a24bf91ecc33837 > > > If I revert that one, I have my 50 M/s back. config and dmesg attached > in case they're useful. Wow.. same deal here -- sequential throughput drops from 40MB/sec to 28MB/sec with CFQ -- whereas the anticipatory scheduler maintains the 40MB/sec. Jens.. I wonder if the new merging test is a bit too strict? There are four possible combinations, and the new code allows merging for two of them: sync+sync and async+async. But surely one of (not sure which) sync+async or async+sync may also be okay? Or would it? This is a huge performance hit. Cheers - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/